M. hungateiproduces methane by growing on CO2-H2 or formate. Acetate that can be utilized as a carbon source (Ekiel et al. 1983), acts as a chemotactic stimulator to this strain (Migas et al., 1989). M. hungatei serves an important role as the terminal member in syntrophic associations facilitating growth on propionate with Syntrophobacter spp. and on lactate and other organic substrates withDesulfovibriospp. in absence of sulfate (Boone and Bryant, 1980; Wallrabenstein et al., 1994). Thus M. hungatei is a keystone species in carbon cycling and biodegradation of organic substrates both in sewage treatment facilities and in natural ecosystems. M. hungatei has been recently confirmed as an important mercury methylator converting less toxic inorganic mercury into the neurotoxicant methylmercury under mineral-limited anaerobic conditions (Yu et al., 2013), consistent with the presence of putative Hg methylation genes in its genome (Parks et al., 2013).